The present invention relates generally to vent valves for locally venting a brake pipe of a air brake system vehicle in response to an emergency brake application and more specifically to an emergency vent valve to be used in combination with an improved control valve.
With the advent of longer and longer trains, vent valves are included in the brake pipe to accelerate the application of an emergency signal through the train to the various control valves. This is an effort to decrease the transmission time of the emergency signal down the brake pipe and to have the brakes apply as simultaneously as possible. It should be noted that the vent valves have been used in combination with control valves which include a service and an emergency portion. The emergency portion not only applies an emergency brake valve to the brake cylinder, but also locally vents the brake pipe in response to an emergency brake application.
Vent valves have operated on two principles of operation. In both principles of operation, a control volume pressure is reduced to match the reduction of the brake pipe at a service rate to prevent the vent valve from operating. When the brake pipe reduction is at a emergency rate, the reduction of pressure in the control volume cannot keep up and a differential pressure is created across a piston which operates the vent valve. The control volume using one principle is vented to atmosphere and using the other principle is vented to the brake pipe.
When the control volume is vented to brake pipe, there is usually a restriction which defines the rate of flow which differentiates between the service and the emergency brake application. This restriction generally interconnects the two sides of the piston which operates the vent valve. This method of operation is sensitive to different pressures carried in the train brake pipe and thus is less desirable. These include #8 vent valve, KMZ vent valve and VX vent valve in use today.
Where the control volume is vented to atmosphere, a valve is provided to throttle the exhaust of the control chamber to atmosphere during a service brake application in accordance with the actual rate of brake pipe pressure reduction. Once the brake application is terminated, the exhausting of the control chamber to atmosphere must also be terminated.
While most recent designs are directed to exhausting the control chamber to brake pipe, there is a need to return to the technology wherein the control volume is vented to atmosphere directly. This will increase the controllability of and the use of the brake pipe as a control throughout the train.
Thus, it is an object of the present invention to provide an improved emergency vent valve which exhausts the control volume to atmosphere.
These and other objects are achieved by providing an emergency vent valve which has a control volume, a piston response to the differential pressure between brake pipe and the control volume to operate a vent valve and an exhaust valve responsive to a differential pressure between brake pipe and control volume to connect the control volume to atmosphere. Further included is a first choke for releasing fluid from said control volume at a first or service rate when the exhaust valve is open and a second choke for limiting the release of fluid from said control volume to atmosphere to second or blow down rate less than the first rate when the vent valve and exhaust valve are both open.
A choke valve connects the control volume to atmosphere through the second lower rate choke when opened by the piston. The choke valve connects the second choke in series with the first choke. The first choke is a passage between the exhaust valve and a bore. The choke valve is a spool valve connected to the piston and slides in the bore. The bore is the interior of a bushing and the first choke is in the bushing. The second choke is in the spool valve. The choke valve connects the second choke in series with the first choke when the vent valve and the exhaust valve are fully opened.
The piston is connected to a vent valve by a loss motion. A charging choke is provided in the piston for charging the control volume from the brake pipe. The exhaust valve is a diaphragm valve and includes a spring biasing the diaphragm valve closed. A housing has a brake pipe port and an exhaust port. The control volume, a piston, exhaust and vent valves as well as first and second choke are all provided in the housing.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.